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Subject: Re: [OMPI users] is loop unrolling safe for MPI logic?
From: Eugene Loh (eugene.loh_at_[hidden])
Date: 2010-07-17 12:14:11


Jeff Squyres wrote:

>On Jul 17, 2010, at 4:22 AM, Anton Shterenlikht wrote:
>
>
>>Is loop vectorisation/unrolling safe for MPI logic?
>>I presume it is, but are there situations where
>>loop vectorisation could e.g. violate the order
>>of execution of MPI calls?
>>
>>
>I *assume* that the intel compiler will not unroll loops that contain MPI function calls. That's obviously an assumption, but I would think that unless you put some pragmas in there that tell the compiler that it's safe to unroll, the compiler will be somewhat conservative about what it automatically unrolls.
>
>
More generally, a Fortran compiler that optimizes aggressively could
"break" MPI code.

http://www.mpi-forum.org/docs/mpi-20-html/node236.htm#Node241

That said, you may not need to worry about this in your particular case.